It doesn't matter how much you want to continue riding beating a dead horse is not going to get you anywhere.

If something is already done and over with there is no point in still talking about it.

If something is already broken there is no point in trying to use it.

Someone breaks up with there girl/boyfriend and continues to bitch about them to there friends weeks later. That person is beating a dead horse, the relationship is over there is no point in thinking about it since the matter is already resolved with you having broken up.

Relationship = dead horse
Bitching about it = beating it

Trying over and over to start your car after you've been in an accident where it is clear that the car is not going to work.

A government study was funded to study various sexual perversions: sado-masochism, necrophilia and bestiality. The study was soon halted however ... the researchers decided they were just beating a dead horse.